Conventionally, a device for determining a driver's inattentive driving (driving without looking ahead) by a method as described below has been proposed (see PTL 1). The conventional device captures an image of the face of the driver by, for example, a camera, and detects the direction of the driver's face or gaze. When the detected direction is within a predetermined range, and moreover, the detection period is within a predetermined period, the conventional device determines that the driver is performing inattentive driving.